Polymeric vehicle for coatings

ABSTRACT

This invention relates to a polymeric vehicle comprising a modified polymer containing covalently bonded mesogenic groups. The modified polymer may be used as the sole component of the polymeric vehicle for a coating to which may be added solvents and known additives to provide a formulated coating. The polymeric vehicle may further include other modified or unmodified polymers and cross-linking resins. The polymeric vehicle provides a coating binder and coating film of high hardness, flexibility and impact resistance.

This application is a continuation of application Ser. No. 695,421,filed on May 3, 1991, now U.S. Pat. No. 5,244,699, which is a divisionalof Ser. No. 170,907, filed on Mar. 21, 1988, now U.S. Pat. No.5,043,192, which is a continuation-in-part of application Ser. No.168,231, filed on May 15, 1988, now abandoned, which is acontinuation-in-part of application Ser. No. 86,504, filed on Aug. 14,1987, now abandoned, which is a continuation-in-part of applicationsSer. Nos. 31,395 and 31,397, both filed on Mar. 27, 1987, both nowabandoned.

BACKGROUND OF INVENTION

Liquid-crystal (L-C) polymers are known to form mesophases having one-and two-dimensional order as disclosed by Flory, P. J., Advances inPolymer Science, Liquid Crystal Polymers I; Springer-Verlag: New York(1984) Volume 59; Schwarz, J. Mackromol, Chem. Rapid Commun. (1986) 7,21. Further, mesophases are well known to impart strength, toughness andthermal stability to plastics and fibers as described by Kwolek et al inMacromolecules (1977) 10, 1390; and by Dobb et al, Advances in PolymerScience, Liquid Crystal Polymers II/III (1986) 255(4), 179.

While L-C polymers have been widely studied, their potential utility ascoatings binders seems to have been overlooked. Japanese patentsclaiming that p-hydroxybenzoic acid (PHBA), a monomer commonly used inL-C polymers, enhances the properties of polyester powder coatings areamong the very few reports that may describe L-C polymers in coatings;Japanese Kokai 75/40,629 (1975) to Maruyama et al; Japanese Kokai76/56,839 (1976) to Nakamura et al; Japanese Kokai 76/44,130 (1976) toNogami et al; and Japanese Kokai 77/73,929 (1977) to Nogami et al.

Hardness and impact resistance are two desirable characteristics ofcoatings. However, because hardness is associated with higher T_(g) s(glass transition temperatures), and good impact resistance with lowerT_(g) s, there is usually a trade-off between hardness and impactresistance. Further, non-baked polymeric vehicles with low viscositieswhich provide binder coating films with improved hardness and shorterdrying times through combinations of polymers with mesogenic groups arenot disclosed in the prior art and are to be desired.

An object of this invention is the provision of modified polymerscomprising low T_(g) polymers covalently bonded with mesogenic groupsfor use in formulated coatings to provide improved films.

A more particular object of this invention is to provide enamels ofimproved hardness and impact resistance.

Other important objects are to provide high solids/low viscosity,non-baking formulated coatings comprising polymeric vehicles forproviding films wherein the coating formulation is fast drying andprovides hard and impact resistant films.

Still further objects and advantages of the invention will be found byreference to the following description.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 outlines the synthesis of modified alkyds.

FIG. 2 provides a thermogram of a modified alkyd.

FIG. 3 shows the effect of PHBA (parahydroxybenzoic acid) content inalkyd resins has on viscosity.

FIG. 4 shows the effect that solution solid content has on viscosity foralkyd resins.

FIG. 5 outlines the synthesis of modified acrylic copolymers.

FIG. 6 outlines the synthesis of modified acrylic copolymers withspacers.

FIGS. 7 and 8 show the effect that solution solid content has onviscosity for acrylic resins.

FIG. 9 shows phase diagrams for modified acrylic copolymers.

FIG. 10 shows thermograms of modified diols.

DESCRIPTION OF THE INVENTION

In accord with this invention a polymeric vehicle is prepared, thepolymeric vehicle comprising a modified polymer containing covalentlybonded mesogenic groups. This modified polymer may be used as the solecomponent of a polymeric vehicle for a coating, to which may be addedsolvents and known additives such as pigments, thereby providing aformulated coating. Optionally the polymeric vehicle comprises amodified polymer in a mixture with other polymers, modified orunmodified, and with cross-linking resins. Solvents and additives may beadded to such a mixture of polymers and resins to make a formulatedcoating. An aspect of the invention is provision of a coating binderwhich is the polymer portion which includes the modified polymer, of acoating film which has high hardness, flexibility, and impactresistance. After the formulated coating is applied to a base orsubstrate, solvents (if present) evaporate leaving a solvent-free film.Evaporation may be accelerated by heating, as by baking. In some formsof the invention, no further chemical reaction is necessary to impartuseful properties to the resulting solvent-free film. In other forms ofthe invention, optimum properties are attained only after chemicalreactions occur within the film, forming covalent bonds and increasingthe molecular weight of the modified polymer and usually converting itinto a three-dimensional cross-linked polymeric network. In some casesthese chemical reactions occur between the modified polymer and across-linking resin if present in the formulated coating. In othercases, the modified polymer may chemically react with substances towhich the film is exposed after solvent evaporation, for example, withoxygen in the air. The chemical reactions that form a cross-linkednetwork may be accelerated by heating (baking). It is the provision ofthis improved film with improved hardness, flexibility and impactresistance, and the coating binder therefor, to which this invention isparticularly directed. Since the coating binder primarily provides thedesired film characteristics, the properties of the coating binder areparticularly described primarily by tests which measure hardness andimpact resistance.

This invention provides for using a polymeric vehicle comprising amodified polymer which after film formation provides a low T_(g) coatingbinder which has hardness and impact resistance. We have found that thepresence of mesogenic groups covalently bonded to otherwise amorphouspolymers provides coating binders that are substantially harder thancomparable coating binders not having mesogenic groups and have foundthat this is obtained without substantially raising T_(g) of the coatingbinder. The presence of covalently bound mesogenic groups also impartsother desirable properties to the formulated coating. Thus, according tothe invention, it is possible to prepare very hard coating binders andfilms while retaining the impact resistance, flexibility and adhesionassociated with a low T_(g). Coating binders with T_(g) s in a rangefrom -50 degrees C. to +10 C. are often very elastic and impactresistant, but they are generally too soft to be useful in most coatingsapplications. On the other hand, non-crosslinked coatings with T_(g) sabove 60 degrees C. are usually hard, but they are generally brittle andhave very poor impact resistance. It is, therefore, beneficial to imparthardness to coating binders without sacrificing impact resistance.Moreover, the presence of covalently bound mesogenic groups impartsother desirable properties to the formulated coating. For example, thisinvention can alleviate a common problem of formulated coatings: thatsubstantial amounts of solvent are required to reduce viscosity to alevel low enough for application of polymers whose T_(g) s and molecularweights are high enough to provide good properties. The use of largeamounts of solvent results in increased costs and often in unacceptablelevels of atmospheric pollution. Especially large amounts of solvent areoften required for conventional coatings vehicles whose T_(g) s andmolecular weight are high enough to impart desirable properties withoutcross-linking. Presence of mesogenic groups can both improve theirproperties and reduce the amount of solvent required.

The groups that provide the coating binder of the invention are called"mesogenic groups". The mesogenic groups of this invention are chemicalstructures that contain a rigid sequence of at least two aromatic ringsconnected in the para position by a covalent bond or by rigid orsemi-rigid chemical linkages. Optionally, one of the rigid aromaticrings may be a naphthalenic rings linked at the 1,5- or 2,6-positions.Modified polymers containing mesogenic groups are called "mesomorphous."The coating binders of this invention contain between 5 percent and 50percent by weight of mesogenic groups to provide the desiredcharacteristics. When a polymer is referred to as "liquid crystalline"herein it is meant to cover such polymer which exhibit mesophases. Thepresence of mesophases are often associated with the presence ofmesogenic groups.

As used in this application, "polymer" means a polymeric or oligomericcomponent of a coating vehicle such as an acrylic polymer or a polyesterpolymer; alkyd polymers are considered to be a sub-class of polyesterpolymers. "Cross-linker resin" means a di- or polyfunctional substancecontaining functional groups that are capable of forming covalent bondswith hydroxyl, carboxyl and --SH groups that are optionally present onthe polymer; aminoplast and polyisocyanate resins are members of thisclass; melamine resins are a sub-class of aminoplast resins. "Modifiedpolymer" means a polymer having covalently bound mesogenic groups asdescribed herein. "Polymeric vehicle" means all polymeric and resinouscomponents in the formulated coating, i.e. before film formation,including but not limited to modified polymers. "Coating binder" meansthe polymeric part of the film of the coating after solvent hasevaporated and, in cases where cross-linking occurs, aftercross-linking. "Formulated coating" means the polymeric vehicle andsolvents, pigments, catalysts and additives which may optionally beadded to impart desirable application characteristics to the formulatedcoating and desirable is formed by application of the formulated coatingto a base or substrate, evaporation of solvent, if present, andcross-linking, if desired. "Air-dried formulated coating" means aformulated coating that produces a satisfactory film without heating orbaking. "Baked formulated coating" means a formulated coating thatprovides optimum film properties upon heating or baking above ambienttemperatures.

Acrylic polymer means a polymer or copolymers of ##STR1## wherein y=CH₃or H

x= ##STR2## or tolyl R=straight chain or branches alkyls having 1 to 12carbons, ##STR3## n=2 to 7.

In the case of hydroxy-substituted alkyl acrylates the monomers mayinclude members selected from the group consisting of the followingesters of acrylic or methacrylic acid and aliphatic glycols: 2-hydroxyethyl acrylate; 3-chloro-2-hydroxypropyl acrylate;2-hydroxy-1-methylethyl acrylate; 2-hydroxypropyl acrylate;3-hydroxypropyl acrylate; 2,3-dihydroxypropyl acrylate; 2-hydroxybutylacrylate; 4-hydroxybutyl acrylate; diethylene-glycol acrylate;5-hydroxypentyl acrylate; 6-hydroxyhexyl acrylate; triethyleneglycolacrylate; 7-hydroxyheptyl acrylate; 2-hydroxy-1-methylethylmethacrylate; 2-hydroxy-propyl methacrylate; 3-hydroxypropylmethacrylate; 2,3-dihydroxypropyl methacrylate; 2-hydroxybutylmethacrylate; 4-hydroxybutyl methacrylate; 3,4-dihydroxybutylmethacrylate; 5-hydroxypentyl methacrylate; 6-hydroxyhexyl methacrylate;1,3-dimethyl-3-hydroxybutyl methacrylate; 5,6-dihydroxyhexylmethacrylate; and 7-hydroxyheptyl methacrylate.

"Polyester polymers" means the polymerized reaction product of polyacidsand polyols; polyacids include diacids such as isophthalic,terephthalic, and fumaric acids and HOOC(CH₂)_(n) COOH where n=2 to 14and "dimer acids", anhydrides of diacids such as maleic, phthalic,hexahydrophthalic, and succinic, and anhydrides of polyacids such astrimellitic acid anhydride. The polyols include linear diols such asHO(CH₂)_(m) OH where m=2 to 16, branched aliphatic diols such asneopentyl glycol, 1,3-butylene glycol, propylene glycol and1,3-dihydroxy-2,2,4-trimethylpentane, cycloaliphatic diols such ashydroquinone, 1,4-dihydroxymethylcyclohexane and "hydrogenated bisphenolA", diol ethers such a diethylene glycol, triethylene glycol anddipropylene glycol, and polyols such as glycerol, pentaerythritol,trimethylol propane, trimethylol ethane, dipentaerythritol, sorbitol andstyrene-allyl alcohol copolymer.

Esterification catalysts that are used in the process for preparingpolyesters are butyl stannoic acid, barium oxide, barium hydroxide,barium naphthenate, calcium oxide, calcium hydroxide, calciumnaphthenate, lead oxide, lithium hydroxide, lithium naphthenate, lithiumrecinoleate, sodium hydroxide, sodium naphthenate, zinc oxide, and leadtallate with butyl stannoic acid being preferred.

In this invention "alkyd polymers" are considered to be a sub-class of"polyester polymers." Alkyds are condensation polymers of the polyacidsand polyols as described above that also contain monobasic acids. Themonobasic acids may include saturated or unsaturated fatty acids havingbetween 9 and 26 carbon atoms and monobasic aromatic acids.

Fatty, or other carboxylic, acids that are used to prepare alkyd resinsinclude HOOC(CH₂)_(n) CH₃ where n=7 to 22, oleic acid, linolelic acid,linolenic acid, erucic acid, soybean oil fatty acids, linseed oil fattyacids, safflower oil fatty acids, sunflower oil fatty acids, coconut oilfatty acids, tall oil fatty acids, dehydrated castor oil fatty acids,benzoic acid, toluic acid and t-butylbenzoic acid. Fatty acids may beincorporated into the alkyd polymer as such or as a component oftriglycerides.

Although it is especially important that covalently bonded mesogenicgroups, according to the invention, impart substantially improvedhardness to coating binders without sacrificing impact resistance, themesogenic groups often improve coatings in at least two other ways. Insome cases inclusion of modified polymers according to the inventioneffectively lowers the viscosity of formulated coatings at a givensolids content relative to the viscosity of comparable unmodifiedpolymers in comparable solvents at the same solids level. The reason isthat mesogenic groups tend to cause modified polymers to form stabledispersions rather than solutions in many common solvents. Thus, lesssolvent is required, reducing cost and air pollution. Furthermore, inthe case of air dried formulated coatings, the mesogenic groups greatlyreduce the time necessary for the polymeric vehicle to harden into afilm, referred to as "dry-to-touch" time.

We have found that mesogenic groups covalently bound to polymers canimprove polymeric vehicles which provide coating binders having a T_(g)as low as -50° C. or as high as +60° C. while providing improvedhardness, adhesion, impact resistance and flexibility.

In accord with this invention, mesogenic groups in various forms areused to modify polymers for polymeric vehicles thereby providing filmswith desired characteristics. The polymeric vehicle comprises a modifiedpolymer in the range of from about 100 to about 35 weight percent basedupon the weight of the polymeric vehicle, and unmodified polymers and/orcross-linking resins in the range of from about 0 to about 65 weightpercent based upon the polymeric vehicle. The modified polymer is anacrylic polymer or a polyester polymer to which mesogenic groups arecovalently bound such that the coating binder contains from about 5 toabout 50 weight percent mesogenic groups, based upon the weight of themodified polymer. The mesogenic groups are selected from the groupconsisting of ##STR4## u=X m=an integer from 2 to 8;

n=1 or 2;

p=an integer from 1 to 4; and

q=an integer from 1 to 3.

The mesogenic groups may be reacted with the polymer as seen in theexamples.

When one of the reactive constituents of the mesogenic groups are notreacted with the polymer they are terminated by --H, --CN, --COOR,--OOCR and --OR wherein R is H, alkyl (which is straight chained orbranched) having 1 to 12 carbon atoms or aryl such as having from 6 to12 carbon atoms.

The polymeric vehicle provides a coating binder having a Tg not greaterthan about 60° C. as measured by Differential Scanning Colorimetry(DSC); and, at a thickness of about 1 mil, the coating binder has apencil hardness of a t least about "H" and a reverse impact resistanceof at least about 30 inch-pounds. Films which include coating bindergenerally will range from about 0.05 mil to about 50 mil in thickness,but hardness and impact resistance may vary with the thickness of thefilm; hence hardness and impact resistance are described at a thicknessof about 1 mil.

An important aspect of the invention is when the modified polymer iscross-linked. It may be cross-linked with a cross-linking resin selectedfrom the group consisting of aminoplast resins, polyisocyanate resins,and mixtures thereof; melamine resins are a sub-class of aminoplastresins; optionally, the isocyanate groups of the polyisocyanate resinmay be blocked with active hydrogen compounds such as alcohols, phenols,oximes and lactams. In one important embodiment an aminoplast orpolyisocyanate resin cross-links a modified polymer which is a a polyolor contains pendant or terminal --COOH or --SH groups. In one importantembodiment the polyol has the general formula: ##STR5## Wherein, x=1 to10; ##STR6## R'= O(CH₂)_(n) O,

O[(CH₂)_(n) O]_(m), ##STR7## {O[(CH₂)₅ COO]_(p) R""}₂, orO[R"OOCR'"COO]_(p) R"O;

R" and R""=a aliphatic or cycloaliphatic radical having 12 carbon atomsor less;

R'"=aromatic radical having 10 carbon atoms or less,

cycloaliphatic radical having 12 carbon atoms or less,

or an aliphatic radical having 36 carbon atoms or less;

n=5 to 16; m=2 to 200; and p=1 to 20.

In an alternate embodiment of the invention the modified polymer is apredominately phenolic oligoester polyol which is cross-linked with amelamine or polyisocyanate resin. In this embodiment the modifiedpolymer (the oligoester polyol) is a reaction product ofp-hydroxybenzoic acid (PHBA) and a non-liquid crystal linear oligoesterdiol which is a reaction product of a heated mixture of

(a) phthalic acid (PA), isophthalic acid, terephthalic acidhexahydrophthalic anhydride;

(b) an aliphatic dicarboxylic acid having a carbon chain length of from4 to 36, such as adipic acid (AA); and

(c) aliphatic primary or secondary diols, the aliphatic chain havingfrom 2 to 23 carbons, such as neopentyl glycol.

A procedure particularly successful in the production of oligoesterpolyols for this embodiment of the invention involves production of thenon-modified linear oligoester polyol resin by reacting the aliphaticdicarboxylic acid having a carbon chain length of from 4 to 36, thealiphatic primary or secondary diol or polyol having the carbon chainlength of from 2 to 23, and one or more of the dicarboxylic acids of (a)above. PHBA is then covalently bonded to this non-modified oligoesterpolyol using p-toluenesulfonic acid (p-TSA); thereby providing theoligoester polyol or modified polymer which cross-links with themelamine or polyisocyanate. The reasons that this procedure isconsidered particularly successful and preferred are:

(1) it can be used in large scale production; and (2) the use of p-TSAreduces the yield of by-product phenol and raises the yield of thedesired modified polymer. In this embodiment, the weight ratio of PHBAto the non-mesogenic portion of the linear diol is in the range of fromabout 20/80 to about 60/40.

Another important aspect of the invention arises in cases where themesogenic groups are bonded to acrylic or polyester polymers by graftpolymerization to prepare modified polymers. In this aspect,non-mesogenic acrylic and polyester polymers containing reactive groupssuch as --COOH and --OH are synthesized. The reactive groups serve assites for grafting.

Especially preferred are grafting sites consisting of --COOH groups.Acrylic polymers containing such groups can be prepared by including--COOH functional monomers such as (meth)acrylic acid among the monomersused to prepare the acrylic monomer. Polyester resins with --COOH groupscan be synthesized by using an excess of polyacid monomers over polyolmonomers. Alternatively, --OH functional acrylic and polyester polymerscan be provided with --COOH functional groups by reacting them withspacers such as diacids such as adipic, isophthalic or terephthalicacids or with cyclic anhydrides such as phthalic, succinic or maleicanhydrides. It is advantagous in some circumstances to convert --OHgroups to --COOH groups because some reactants graft more readily to--COOH groups.

p-Hydroxybenzoic acid, PHBA, is a commonly used component of themesogenic group in modified polymers. It may be grafted to acrylic orpolyester polymers having --OH or --COOH groups; the latter arepreferred. A typical grafting process is shown in FIG. 1. In this casethe mesogenic groups grafted onto the polymer to form the modifiedpolymer are oligomeric PHBA having the general formula: ##STR8## wheren=2 to 8 and preferably the number average degree of polymerization ofgraft segments is between about 2.0 to about 6.0. See Tables 13 a-h formesogenic examples. See Tables 13 a-c (Mono-functional Derivates), 13d-g (Di-Functional Derivates), 13 h (Miscellaneous Derivatives) for adescription of specific mesogenic groups of the invention.

The modified polymer may comprise the entire polymeric vehicle, it maybe blended with other polymers and/or with cross-linking resins, or itmay be cross-linked by substances to which the film is exposed afterapplication. In cases where the modified polymer is not cross-linked, itshould have a number average molecular weight (Mn_(n)) above about10,000 for modified acrylic polymers and about 7,000 for modifiedpolyester polymers. Preferred ranges are about 15,000 to 10⁶ foracrylics and about 10,000 to 10⁵ for polyesters. When the modifiedpolymers undergo chemical reactions after

                  TABLE 13a                                                       ______________________________________                                        Monofunctional Derivatives                                                    ______________________________________                                         ##STR9##                     M1                                               ##STR10##                    M2                                               ##STR11##                    M3                                               ##STR12##                    M4                                               ##STR13##                    M5                                               ##STR14##                    M6                                               ##STR15##                    M7                                               ##STR16##                    M8                                               ##STR17##                    M9                                               ##STR18##                    M10                                              ##STR19##                    M11                                              ##STR20##                    M12                                              ##STR21##                    M13                                              ##STR22##                    M14                                              ##STR23##                    M15                                              ##STR24##                    M16                                             ______________________________________                                    

                  TABLE 13b                                                       ______________________________________                                        Monofunctional Derivatives                                                    ______________________________________                                         ##STR25##                    M17                                              ##STR26##                    M18                                              ##STR27##                    M19                                              ##STR28##                    M20                                              ##STR29##                    M21                                              ##STR30##                    M22                                              ##STR31##                    M23                                             ______________________________________                                    

                  TABLE 13c                                                       ______________________________________                                        Monofunctional Derivatives                                                    ______________________________________                                         ##STR32##                    M24                                              ##STR33##                    M25                                              ##STR34##                    M26                                              ##STR35##                    M27                                              ##STR36##                    M28                                              ##STR37##                    M29                                              ##STR38##                    M30                                              ##STR39##                    M31                                             ______________________________________                                    

                  TABLE 13d                                                       ______________________________________                                        Difunctional Derivatives                                                      ______________________________________                                         ##STR40##                     D1                                              ##STR41##                     D2                                              ##STR42##                     D3                                              ##STR43##                     D4                                              ##STR44##                     D5                                              ##STR45##                     D6                                              ##STR46##                     D7                                              ##STR47##                     D8                                              ##STR48##                     D9                                             ______________________________________                                    

                                      TABLE 13e                                   __________________________________________________________________________    Difunctional Derivatives                                                      __________________________________________________________________________     ##STR49##                                           D10                       ##STR50##                                           D11                       ##STR51##                                           D12                       ##STR52##                                           D13                       ##STR53##                                           D14                       ##STR54##                                           D15                       ##STR55##                                           D16                       ##STR56##                                           D17                      __________________________________________________________________________

                                      TABLE 13F                                   __________________________________________________________________________    Difunctional Derivatives                                                      __________________________________________________________________________     ##STR57##                              D18                                    ##STR58##                              D19                                    ##STR59##                              D20                                    ##STR60##                              D21                                    ##STR61##                              D22                                    ##STR62##                              D23                                    ##STR63##                              D24                                    ##STR64##                              D25                                   __________________________________________________________________________

                  TABLE 13G                                                       ______________________________________                                        Difunctional Derivatives                                                      ______________________________________                                         ##STR65##                    D26                                              ##STR66##                    D27                                              ##STR67##                    D28                                              ##STR68##                    D29                                              ##STR69##                    D30                                              ##STR70##                    D31                                              ##STR71##                    D32                                             ______________________________________                                    

                  TABLE 13H                                                       ______________________________________                                        Miscellaneous Derivatives                                                     ______________________________________                                         ##STR72##                    Mi1                                              ##STR73##                    Mi2                                              ##STR74##                    Mi3                                              ##STR75##                    Mi4                                              ##STR76##                    Mi5                                              ##STR77##                    Mi6                                              ##STR78##                    Mi7                                              ##STR79##                    Mi8                                              ##STR80##                    Mi9                                              ##STR81##                    Mi10                                             ##STR82##                    Mi11                                             ##STR83##                    Mi12                                             ##STR84##                    Mi13                                             ##STR85##                    Mi14                                             ##STR86##                    Mi15                                             ##STR87##                    Mi16                                             ##STR88##                    Mi17                                             ##STR89##                    Mi18                                            ______________________________________                                         application they may have lower M.sub.n. Preferred ranges of M.sub.n are     from about 1,000 to 50,000 for cross-linkable modified acrylic copolymers     and about 500 to 20,000 for cross-linkable modified polyester copolymers.     Cross-linking is effective for baked and non-baked films.

If the film is to be baked, the modified polymer and cross-linkingresin, such as aminoplasts and blocked isocyanates, may be combined ascomponents of the coating formulation. Reaction of the modified polymerand such cross-linking resins is normally very slow until the coating isapplied and baked. When highly reactive cross-linking resins such apolyisocyanate resins are used, it is usually desirable to mix thecomponents within a few hours of the time of application. Such coatingsrequire little or no baking. Cross-linking may also be effected byexposure of the film to reactants, such as oxygen, after application; insuch cases baking is optional.

The following examples set forth methods of imparting the desiredcharacteristics to polymeric binders and to films. In these examples theproperties of coatings containing modified polymers are compared tothose containing similar non-modified polymers in order to demonstratethe improvements of the invention: 1) a lowered solution viscosity, 2) ahard, adherent, flexible film having excellent impact resistance and 3)greatly reduced dry-to-touch time in the case of air-dried coatings.

EXAMPLE 1

This example concerns model alkyd resins made by a synthetic procedure.The example involves grafting oligomeric esters of p-hydroxybenzoic acid(PHBA) or of PHBA/terephthalic acid (TPA) to alkyd resins so that liquidcrystalline phases are formed. Here the objective is to demonstrate theusefulness of L-C alkyds.

Materials

Linoleic acid (Emersol 315, Emery Ind. Inc., equivalent weight 288) wasdried with anhydrous Na₂ SO₄. Pyridine (Aldrich) was distilled and driedwith anhydrous Na₂ SO₄. All other materials (Aldrich) were used asreceived.

Synthesis of Grafted Model Alkyds G1-G5

Synthesis of grafted PHBA-modified alkyds is outlined in FIG. 1.

(A.) Preparation of unmodified alkyd U1. A low molecular weight modelalkyd, U1, with 55% oil length and 22% OH excess was prepared from 25.00g (0.0868 mol) of linoleic acid, 10.70 g (0.0722 mol) of phthalicanhydride, and 12.61 g (0.094 mol) of trimethylolpropane using theDCC-p-TSA process described by Kangas, S. and Jones, F. N., "Model alkydresins for higher-solids coatings, I", J. Coat. Technol., 59(744), 89(1987). DCC is dicyclohexyl carbodiimide. Yield was 85%. The OH valuewas 56 mg-KOH/g determined by the phthalic anhydride/pyridine method.

(B1.) Modification with succinic anhydride. Alkyd U1 was heated withsuccinic anhydride (one mol per equiv OH) in pyridine at 80° C. for 12hr. The solution was concentrated; the residue was dissolved in CH₂ Cl₂and washed with 10% aq. HCl. The CH₂ Cl₂ layer was concentrated and theresidue was vacuum dried at 80 C. Yield of resin was above 90%; acidnumber was 64 mg-KOH/g.

(B2.) Modification with terephthalic acid (TPA). A solution of 10.0 g(0.010 equiv) of alkyd U1, 8.51 g (0.050 mol) of terephthalic acid, TPA,2.27 g (0.011 mol) of DCC and 0.11 g of p-TSA in 150 ml of pyridine wasstirred at 25 C. for 12 hr. The mixture was filtered to remove DCU andexcess TPA. The filtrate was concentrated, dissolved in CH₂ Cl₂, washedwith 10% aq. HCl and concentrated as above. Traces of crystallinematerial were removed by dissolving the residue in 1/1 pentane/ethylacetate, cooling in a freezer, filtering, reconcentrating and vacuumdrying at 80 C. Yield was 9.62 g of resin; acid number was 62 mg-KOH/g.

(C.) Grafting to form alkyds G1-G5. The intermediate step of reactingalkyd U1 with succinic anhydride or with TPA is desirable to improvegrafting efficiency. This step converts --OH groups of U1 to --COOHgroups; grafting to --COOH groups is more efficient. The succinicanhydride modified alkyd was grafted or covalently bonded with PHBAusing the DCC-p-TSA/pyridine process. Weight ratios (PHBA/alkyd) of 0.1,0.2, 0.3 and 0.5 gave alkyds G1-G4 respectively. For example, thesynthesis on alkyd G2 is described:

A solution of 10.0 g (0.0114 equiv) of carboxyl-terminated model alkyd(prepared as described in B1, above), 2.0 g (0.0145 mol) of PHBA, 3.14 g(0.0152 mol) of DCC, and 0.16 g of p-TSA in 120 ml of pyridine wasstirred at 25 C. for 12 hrs. The product (10.2 g, 85% yield) wasisolated essentially as described immediately above in the TPA reaction.

TPA modified alkyd prepared as described in B2 was covalently bonded bya similar process using a weight ratio (PHBA/alkyd) of 0.5 to give alkydG5. Modification with TPA has the additional advantage of putting halfthe structure needed for liquid crystal formation into place.

Synthesis of "Random" Model Alkyds R1-R3

A series of random model alkyds R1, R2 and R3 containing 15%, 22% and27% by weight in the feed were prepared from linoleic acid, phthalicanhydride, trimethylolpropane, and PHBA in a single step by theDCC-p-TSA process. These weight percents correspond roughly to theweight percents of PHBA actually incorporated in alkyds G2, G3 and G4,respectively. For example, preparation of R3 is described:

A solution of 5.50 g (0.0190 mol) of linoleic acid, 2.54 g (0.017 mol)of phthalic anhydride, 2.91 g (0.022 mol) of trimethylolpropane, 4 g(0.029 mol) of PHBA, 12.24 g (0.060 mol) of DCC, and 0.612 g of p-TSA in200 ml of anhydrous pyridine were mixed in a 250 ml flask for 12 hrs. at25 C. Alkyd R3 was isolated essentially as described above in the TPAreaction.

Alkyd Structure Characterization

¹ H-NMR spectra were determined at 34 C. using a Varian Associates EM390 NMR spectrometer with Me₄ Si as internal standard. IR spectra wererecorded on a Perkin-Elmer 137 spectromphotometer using a 20 weightpercent solution in CH₂ Cl₂.

Differential scanning calorimetry (DSC) was effected with a du Pontmodel 990 thermal analyzer at a heating rate of 20 C./min using samplesthat had been vacuum dried at 80 C. to constant weight. T_(g) wasassigned as the onset of the endothermic inflection. Clearing points(T_(cl)) of L-C phases were assigned as the maxima of the endothermicpeaks.

Equivalent weight per carboxyl group was determined by titration ofpyridine solution with KOH/CH₃ OH to the phenolphthalein end point.

Number average molecular weight (M_(n)), weight average molecular weight(M_(w)), and polydispersity index (PDI=M_(w) /M_(n)) were measured bygel permeation chromatography (GPC) in tetrahydrofuran using a Watersmodel 510 pump, a R401 refractive index detector and a model M730 datamodule; columns were Ultrastyragel 100 A, 500 A, 10³ A, and 10⁴ A.Monodisperse polystyrene calibration standards were used.

Optical textures were examined with a Leitz D-6330 polarizing microscopeequipped with a Reichert hot stage.

Grafting efficiency (GE %) and average number of PHBA units per COOHwere estimated from equivalent weight difference as described in Chen,D. S. and Jones, F. N., "Graft-copolymers of p-hydroxylbenzoic acid,Part I, A general method for grafting mesogenic groups to oligomers", J.Polym. Sci., Polym. Chem. Ed., Vol. 25, pg. 1109-1125 (1987).

Measurement of Viscosity and Tests of Films Properties

Solution viscosity was measured in xylene using an ICI cone and plateviscometer at 25 C. Films were prepared by dissolving or dispersingresins and driers in xylene and casting films on untreated rolled steelpanels by a casting bar to give the dry thickness of 0.5 ml.

Dry-to-touch time was measured according to ASTM D1640. Film propertieswere measured after 7 days of drying at ambient temperature. Reverseimpact resistance and pencil hardness were measured according to ASTMD2794 and D3363 respectively; resistance to acetone was measured by thenumber of double rubs to remove trace of film with paper tissue afterthe dropping of acetone on the dry film. Extractability was measured bysubjecting cured films to 8 hr. in a Soxhlet extractor usingtetrahydrofuran.

The equivalent weight per carboxyl, M_(n), M_(w), PDI, and numberaverage PHBA units per carboxyl of the control alkyd and thePHBA-grafted alkyds are shown in Table 1. As PHBA content increasesequivalent weight, M_(n), and M_(w) increase in proportion to the massof PHBA grafted but no more; PDI remains nearly constant. These resultsindicate that little or no coupling of molecules occurs during grafting.Data for "random" alkyds R1-R3 are shown in Table 2.

                  TABLE 1                                                         ______________________________________                                        Characterization of ungrafted                                                 alkyd U1 and PHBA-grafted G1-G4:                                                           U1    G1      G2     G3    G4                                    ______________________________________                                        wt ratio in feed                                                                             --      0.1     0.2  0.3   0.5                                 PHBA/oligomer                                                                 Eq. wt. per COOH                                                                             876*    916     1014 1065  1080                                (g/eq.)                                                                       wt % of PHBA in resin                                                                        --      8.3     14.5 19.4  28.4                                GE %           --      90      89   85    77                                  units of PHBA  --      0.4     1.15 1.58  1.96                                GRAFTED PER COOH                                                              M.sub.n        1425**  1460    1582 1717  1935                                M.sub.w        2086**  2287    2418 2689  2910                                PDI            1.46    1.57    1.53 1.57  1.50                                T.sub.g (C.)   -29     -24     -20  -15   -10                                 T.sub.cl (C.)  --      --      --   --    190                                 ______________________________________                                         *--After grafting with succinic anhydride.                                    **--Before grafting with succinic anhydride.                             

                  TABLE 2                                                         ______________________________________                                        Properties of "random" alkyds:                                                              R.sub.1  R.sub.2                                                                              R.sub.3                                         ______________________________________                                        wt % of PHBA in feed                                                                          15         22     27                                          M.sub.n         1650       1720   1600                                        M.sub.W         2772       2597   2512                                        PDI             1.68       1.51   1.57                                        Tg, C.          -23        -18    -12                                         ______________________________________                                    

IR spectra of the PHBA grafted alkyds are characterized by two sharppeaks at 1610 and 1510 cm⁻¹. ¹ H-NMR spectra show complex peaks in therange of 7.0-8.0 ppm. These spectral features are characteristic of PHBAgrafted polymers. IR of random alkyds R1-R3 also showed two sharp peaksat 1610 and 1510 cm⁻¹.

Onset T_(g) (by DSC) of the unmodified alkyd U1 was -29 C.; PHBA-graftedalkyds G1-G5 had onset T_(g) s at -24, -20, -15, -10, and +17 C.,respectively. DSC traces of the alkyd U1 and grafted alkyds G1-G3 werefeatureless except for the inflection assigned to T_(g) and the broadexothermic peaks due to thermal cross-linking. DSCs of alkyds G4 and G5had sharp endothermic peaks at 190 and 225 C., respectively; these peaksare attributable to the clearing temperature (T_(cl)) of the L-C phases.The DSC thermogram of alkyd G4 is shown in FIG. 2. DSC thermograms ofrandom alkyds R1-R3 are similar to those of alkyds U1, G1, G2, and G3,no endothermic peaks appeared. T_(g) s of R1, R2, and R3 were -23, -18,and -12 C., respectively.

Optical textures of the dried films were examined under a polarizingmicroscope with a hot stage. Films of alkyds U1, G1-G3 and R1-R3 had novisible L-C phases. However, L-C (mesomorphous) phases were clearlyvisible in films of alkyds G4 and G5. The L-C phase in films of alkyd G4disappeared when the specimen was heated above 190 C. and reappearedquickly as it was cooled to around 190 C.

Viscocity and Appeance of Solutions and Dispersions

Alkyds U1, G1-G3 and R1-R3 appeared soluble in commercial xylene at allconcentrations. In contrast, alkyds G4 and G5 formed stable, opaquedispersions in xylene at concentrations of 5 wt % or higher.

The relationship between viscosity and PHBA content of 70/30 (w/w)mixtures of alkyds G1-G4 and R1-R3 in xylene are shown in FIG. 3.Viscosity increases with increasing PHBA content for alkyds G1-G3, butit drops sharply for alkyd G4. This drop is presumably associated withthe tendency of alkyd G4 to form non-aqueous dispersions. On the otherhand, "random" alkyd R3, whose overall composition is similar to that ofG4, has the highest viscosity in the series. The solids/viscosityrelationship of alkyd G4 is shown in FIG. 4.

Dry Time and Film Properties

As shown in Table 3, all PHBA-grafted alkyds dried faster thanunmodified alkyd U1, and drying speed increased with PHBA content.Acceleration of drying is by far the greatest for L-C alkyds G4 and G5.The latter dried very rapidly (in 5 minutes). As shown in Table 4, thedrying speed of "random" alkyds R1-R3 also increased with the PHBAcontent, but the effect was much smaller than observed for their graftedcounterparts G2-G4.

Coatings made from all alkyds had good adhesion. Films made from alkydsU1, G1 G3 and R1-R3 were glossy and transparent, while film from alkydsG4 and G5 were glossy and translucent.

As shown in Table 3, seven-day old films of PHBA-grafted alkyds G1-G5had better reverse impact resistance, were harder, and had slightlybetter acetone resistance than alkyd U1. All these film properties arefavored by higher PHBA content. Alkyd G4 had the best balance ofproperties, while alkyd G5 was the hardest.

                  TABLE 3                                                         ______________________________________                                        Dry-to-touch times and film                                                   properties of U1 and grafted alkyds G1-G5:                                    Alkyd    U1      G1      G2    G3    G4    G5                                 ______________________________________                                        Dry time*                                                                              10 D    5 D     7 H   5.5 H 1 H   5 M                                film                                                                          properties                                                                    hardness 5B      3B      2B    B     H     2H                                 reverse  35      35      40    65    80    45                                 impact                                                                        strength                                                                      (in-lb)                                                                       crosshatch                                                                             100%    100%    100%  100%  100%  100%                               adhesion                                                                      resistance to                                                                          3       5       5     6     8     8                                  acetone                                                                       (rubs)                                                                        film     GL      GL      GL    GL    GL    GL                                 appearance                                                                             TP      TP      TP    TP    TL    TL                                 ______________________________________                                         *dryers = 0.05% Conapthenate + 0.15% Znnaphthenate by weight per resin.       D = day, H = hour, M = minute.                                                GL = glossy, TP = transparent, TL = translucent.                         

Hardness and solvent resistance of films made from "random" alkyds R1-R3improved with increasing PHBA content (Table 4). On the other hand,impact strength decreased with increasing PHBA content.

                  TABLE 4                                                         ______________________________________                                        Dry-to-touch times and film                                                   properties of "random alkyds" R1-R3:                                                        R1      R2      R3                                              ______________________________________                                        Dry time*       5 H       4.5 H   3.5 H                                       Film Properties                                                               Hardness        HB        HB      H                                           reverse impact strength                                                                       80        45      20                                          (in-lb)                                                                       crosshatch adhesion                                                                           100%      100%    100%                                        Resistance to acetone                                                                         3         4       4                                           (number of rubs)                                                              film appearance GL,       GL,     GL,                                                         TP        TP      TP                                          ______________________________________                                         *dryers = 0.05% Conaphthenate + 0.15% Znnaphthenate per resin.                H = hour, GL = Glossy, TP = Transparent.                                 

The data of the above example indicates the improvements made in analkyd coating and resin when mesogenic groups are covalently bonded tothe alkyd.

EXAMPLE 2

This example reports use of mesogenic groups to modify acrylic polymers.The experimental approach was to prepare several series of --COOHfunctional acrylic copolymers in which molecular weight, Tg, andfunctionality were varied and then to graft p-hydroxybenzoic acid (PHBA)to the --COOH groups. The PHBA groups were the mesogenic groups whichimparted the desired L-C characteristics.

Two types of L-C acrylic polymers were synthesized. In type A the PHBAwas grafted to --COOH groups attached directly to MMA/BA/MAA acryliccopolymer backbones (FIG. 5). In type B and 8-unit flexible spacer wasplaced between the copolymer backbone and the PHBA (FIG. 6). Thebehavior of these copolymers as film formers was investigated.

Materials

Monomers were distilled before use. Pyridine was distilled and thendried by stirring with anhydrous Na₂ SO₄. All other reagents (Aldrich)were used as received.

Preparation of COOH-Functional Acrylic Polymers

COOH-functional acrylic polymers were prepared as substrates forgrafting by radical copolymerization in toluene at 90-100 C. undermonomer starved conditions as described by R. A. Gray, J. Coat,Technol., 57, 83 (1985), using azobisisobutyronitrile (AIBN) asinitiator. Substrates for Type A copolymers (FIG. 5) were composed ofmethyl methacrylate (MMA), butyl acrylate (BA), and acrylic acid (AA) ormethacrylic acid (MAA). Substrates for Type B copolymers (FIG. 6) werecomposed of MMA, BA, and 2-hydroxyethyl methacrylate (HEMA); they weremodified to become COOH-functional by treatment with stoichiometricallyequivalent amount of succinic anhydride in pyridine at 80 C.

The following is an example for the preparation of a COOH-functionalacrylic polymer of Type B:

(a). Polymerization: Toluene (57 g) was placed in a 250-ml, 3-neckflask, heated in an oil bath and stirred mechanically. A solution of32.68 g (0.255 mol) of BA, 22.03 g (0.22 mol) of MMA, 3.25 g (0.025 mol)of HEMA, and 0.57 g of AIBN was added dropwise during 3 hr withcontinuous stirring. Temperature was maintained at 95 to 100 C. duringaddition and for 2 hr. thereafter. A solution of 0.2 g of AIBN in 10 gof toluene was added during 10 min, and the temperature was maintainedfor 1 hr. The solution was concentrated on a rotary evaporator and wasvacuum dried at 80 C. The residue (polymer B6) had 5 mol % OHfunctionality (calcd), a T_(g) of 10 C. (calcd) and Mn of 15,400(measured by GPC). Acrylic copolymers of type A were prepared similarly.

b). Modification with succinic anhydride: A solution of 11.45 g (0.005eq OH) of the above polymer and 0.50 g (0.005 mol) of succinic anhydridein 50 g of pyridine was stirred and heated at 80 C. for 12 hr. Thesolution was concentrated; the residue was dissolved in CH₂ Cl₂ andwashed with 10% aq. HCl. The CH₂ Cl₂ layer was concentrated and theresidue was vacuum dried at 80 C. Yield was 92%. Acid number was 24.

Grafting with PHBA

Both types of COOH-functional acrylic copolymers were grafted with PHBAin pyridine at 100 C. for 36 hr by the DCC-p-TSA process. Ratios of molof PHBA to equiv of --COOH ("equivalent ratios") were 3.5, 5.5, and 7.0in order to vary the length of the grafted PHBA segments. ThePHBA-grafted products of Types A and B were designated GA and GBrespectively. The procedure is exemplified by the grafting of succinicanhydride-modified polymer B6 at equivalent ratio of 7.0:

A solution of 11.80 g (0.005 eq COOH) of polymer B6, 4.84 g (0.035 mol)of PHBA, 7.94 g (0.0385 mol) of dicyclohexycarbodiimide (DCC), and 0.40g of p-toluenesulfonic acid (p-TSA) in 150 g of pyridine was stirred at100 C. for 36 hr. The mixture was filtered to remove urea of DCC (DCU)and PHBA oligomers. The filtrate was concentrated, dissolved in CH₂ Cl₂,washed with 10% aq. HCl, and concentrated. Traces of crystallinecontaminates were removed by dissolving the residue in 1:1 pentane-ethylacetate, cooling in a freezer, filtering, reconcentrating, and vacuumdrying at 80 C. Yield was 85%. The combined crystalline by-productsweighed. Grafting efficiency (GE%) was estimated to be 70% indicating anaverage length of PHBA grafts (#PHBA/COOH) of 4.9 PHBA units.

Grafting was effected to give L-C copolymers of Types GA and GB. Thesetypes differ in that the mesogenic PHBA-grafts are attached directly tothe polymer backbone of Type GA copolymers while Type GB copolymers haveeight-atom flexible spacers between the polymer backbone and themesogenic grafts. Individual copolymers were numbered as shown in Tables5 to 11. Grafting efficiency (GE %) was determined gravimetrically. Itranged from about 85% to about 70%. As expected, GE % decreased as theCOOH equivalent ratio of PHBA/acrylic increased.

Average #PHBA/COOH ratios were calculated from GE %. In order to achieve#PHBA/COOH ratios of 3±0.2, 4±0.2, and 5±0.3 it proved necessary to feedPHBA monomer in the ratio of 3.5, 5.5 and 7.0 moles, respectively, tothe grafting reaction.

Structure Characterization

¹ H-NMR spectra, IR spectra, differential scanning calorimetry (DSC),optical textures under polarizing microscope, M_(n), M_(w),polydispersity index, and average #PHBA/COOH ratio were determined asdescribed in Chen and Jones. The term "#PHBA/COOH ratio" refers to thenumber average degree of polymerization of PHBA graft segments actuallyincorporated in the graft copolymer.

X-ray spectra were recorded with a Philip wide angle diffractometer at25° C. Samples for X-ray diffraction studies were dissolved or dispersedin acetone, cast on glass slides, and vacuum dried at 80° C. for 12 hr.

Measurement of Viscosity

Viscosity was measured using an ICI cone and plate viscometer (shearrate 10⁴ s⁻¹) at 25° C. Samples were dissolved or thoroughly dispersedin methylisobutylketone (MIBK) before measuring.

Observation of Solution Appearance

Samples were dissolved or dispersed thoroughly in MIBK and then put intest tubes. Appearance was observed when the test tubes were immersed inan oil bath and equilibrated at different temperatures. Optical texturesof some L-C polymer dispersions were examined under polarizingmicroscope at 25° C.

Tests of Film Properties

Samples were dissolved or dispersed in MIBK and cast on untreated coldrolled steel panels by a casting bar to give the dry film thickness of1.0 ml. Reverse impact strength and pencil hardness were measuredaccording to ASTM D2794 and D3363, respectively.

Characterization of Polymer Structures

The IR spectra of the PHBA grafted acrylics have sharp peaks at 1610cm⁻¹ and 1510 cm⁻¹ assignable to the para aromatic C-H stretching. Thesetwo peaks are characteristic of oligo-PHBA grafted polymers. They areabsent in the ungrafted acrylics.

¹ H-NMR spectra of the PHBA-grafted acrylics show multiple peaks in therange of 7.0-7.3 ppm and 8.0-8.3 ppm, assignable to the aromatic protonsortho to the OH group and to the COOH group, respectively. They areabsent in the ungrafted acrylics.

Characterization of Microstructure

Polarizing microscopy, differential scanning calorimetry (DSC), and wideangle X-ray diffraction (WAXS) were used to further characterize themicrostructures of the graft copolymers in the bulk phase. Results(Tables 5 and 6) were consistent with assignment of L-C microstructureto all polymers except GA21a-c.

                  TABLE 5                                                         ______________________________________                                        Compositions of type A acrylic substrates and type A                          PHBA-grafted acrylic copolymers-                                              ______________________________________                                        (a). Type A acrylic substrates:                                               (a1). The -MMA-BA-AA- series                                                       mol fraction     T.sub.g                                                 #    (MMA/BA/AA)      (°C., calcd.)                                                                     M.sub.n                                      ______________________________________                                        A11  0.274/0.676/0.05 -10        15,700                                       A12  0.355/0.595/0.05 0          28,400                                       A13  0.274/0.676/0.05 -10        4,870                                        A14  0.274/0.676/0.05 -10        9,945                                        A15  0.274/0.676/0.05 -10        14,865                                       A16  0.274/0.676/0.05 -10        28,500                                       A17  0.355/0.595/0.05 0          4,750                                        A18  0.332/0.593/0.75 0          4,810                                        A19  0.309/0.591/0.10 0          5,100                                        A20  0.355/0.595/0.05 0          15,630                                       ______________________________________                                        (a1). The -MMA-BA-MAA- series                                                      mol fraction     T.sub.g                                                 #    (MMA/BA/MAA)     (°C., calcd.)                                                                     M.sub.n                                      ______________________________________                                        A21  0.351/0.549/0.10 10         4,910                                        A22   0.383/0.542/0.075                                                                             10         5,130                                        A23  0.415/0.535/0.05 10         5,490                                        ______________________________________                                        (b). Type GA PHBA-grafted acrylic copolymers:                                 (b1). series from -MMA-BA-AA-                                                 #PHBA/     PHBA content                                                                              T.sub.g T.sub.cl                                       #     COOH     (wt %)      (°C., measured)                                                                  LC phase*                                ______________________________________                                        GA11  4.9       20.0       -2    173   smectic                                GA12  5.1      21.0        -4    175   smectic                                GA13  5.2      21.0        -2    174   smectic                                GA14  5.0      20.3        -3    174   smectic                                GA15  4.9      20.0        -2    173   smectic                                GA16  5.1      20.7        -4    174   smectic                                GA17  4.9      20.3         7    173   smectic                                GA18  5.2      29.0         9    174   smectic                                GA19  4.8      33.6         14   181   smectic                                GA20  4.8      19.8         4    175   smectic                                ______________________________________                                        (b2). Series from -MMA-BA-MAA-                                                #PHBA/     PHBA content                                                                              T.sub.g                                                                             T.sub.m                                                                            T.sub.cl                                    #     COOH     (wt %)      (°C., measured)                                                                  LC phase*                                ______________________________________                                        GA21a 3.2      25.2        16  147  --   crystal                              GA21b 4.1      30.1        22  186  --   crystal                              GA21c 4.9      34.0        25  210  --   crystal                              GA22a 3.0      20.3        15  --   165  smectic                              GA22b 3.8      23.2        13  --   175  smectic                              GA22c 4.8      27.6        20  --   184  smectic                              GA23a 3.1      14.0        14  --   162  smectic                              GA23b 4.0      17.4        15  --   173  smectic                              GA23c 5.1      21.1        17  --   178  smectic                              ______________________________________                                         *--according to optical texture.                                         

                  TABLE 6                                                         ______________________________________                                        Compositions of type B acrylic substrates and type GB                         PHBA-grafted acrylic copolymers--                                             ______________________________________                                        (a). Type B acrylic substrates                                                      mol fraction     T.sub.g                                                #     (MMA/BA/HEMA)    (°C., calcd.)                                                                     M.sub.n                                     ______________________________________                                        B1    0.282/0.668/0.05 -10        14,500                                      B2    0.364/0.586/0.05 0          15,130                                      B3    0.364/0.586/0.05 0           5,050                                      B4    0.364/0.586/0.05 0          10,800                                      B5    0.364/0.586/0.05 0          28,200                                      B6    0.044/0.51/0.05  10         15,420                                      ______________________________________                                        (b). Type GB PHBA-grafted acrylic substrates                                  #PHBA/     PHBA content                                                                              T.sub.g T.sub.cl                                       #     COOH     (wt %)      (°C., measured)                                                                  LC phase*                                ______________________________________                                        GB1   5.0      19.3        -5    171   smectic                                GB2a  4.8      19.0        4     174   smectic                                GB2b  3.2      13.5        3     159   smectic                                GB2c  4.1      16.7        3     164   smectic                                GB3   5.1      19.9        4     175   smectic                                GB4   4.9      19.3        5     174   smectic                                GB5   5.2      20.2        5     174   smectic                                GB6   4.9      19.6        14    177   smectic                                ______________________________________                                         *--according to optical texture.                                         

FIG. 7 shows shear viscosities (shear rate 10⁴ s⁻¹) of MIBK solutions ofthree ungrafted acrylic copolymers and of a dispersion of an L-C graftcopolymer derived from one of them as a function of concentration. Theungrafted copolymers (B1, B2, and B6) differ only in Tg (-10, 0, +10 C.,respectively); all three have M_(n) of about 15,000 and functionality of5 mol %. L-C copolymer GB1 was prepared by grafting B1 with an average#PHBA/COOH ratio of 5.0. As expected, solution viscosities of ungraftedcopolymers increase moderately as T_(g) increases. However, viscosity ofGB1, an anisotropic dispersion throughout most of the concentrationrange studied, was substantially lower than that of the copolymer fromwhich it was made. The viscosity range 0.1 to 0.2 Pa.s (a viscositysuitable for spray application of coatings) was attained at about 40 to45 wt. % with the ungrafted polymers and at about 45 to 50 wt. % withL-C copolymer GB1.

The effect of #PHBA/COOH ratio on viscosity was studied; results areshown in FIG. 8. B2 is an ungrafted acrylic copolymer with M_(n) ofabout 15,000, T_(g) of 0 C., and functionality of 5 mol %. GB2a and GB2bare L-C graft copolymers prepared from B2 with actual #PHBA/COOH ratiosof 4.8 and 3.2, respectively. Again, viscosities of anisotropicdispersions of the grafted copolymers were significantly lower thansolutions of the copolymers from which they were made. It appears thatincreasing #PHBA/COOH ratio slightly reduces viscosity of thedispersions. Viscosity of dispersions of a third L-C copolymer in thisseries, GB2c (#PHBA/COOH ratio=4.1) was intermediate between GB2a andGB2b.

The behavior of L-C copolymer/MIBK mixtures depended on temperature,concentration and #PHBA/COOH ratio. The phase diagrams in FIG. 9 aretypical. Behavior of two copolymers, GB2b (#PHBA/COOH=3.2, dashed line)and GB2a (#PHBA/COOH=4.8, solid line) is shown. These graft copolymersare from the same acrylic copolymer substrate; they differ only in#PHBA/COOH ratio. Both copolymers formed transparent isotropic"solutions" (A) at low concentrations and/or at elevated temperatures.At lower temperatures both copolymers formed biphasic states (B) andanisotropic states (C) at high concentrations. This sort of behavior istypical of lyotropic L-C polymers. Increasing #PHBA/COOH ratio from 3 to5 decreases solubility, shifting the phase diagram by about 10 wt % asshown.

#PHBA/COOH ratio strongly affected the concentrations at phaseboundries. As #PHBA/COOH ratio increases the phase boundaries shift tolower concentrations. Temperature also affect the phase boundaries. Forexample, as shown in FIG. 9, both the biphasic state and the anisotropicstate become isotropic (i.e., they "clear") when heated. The clearingtemperatures increased as the #PHBA/COOH ratios increased.

Properties of cast films of selected L-C acrylic copolymers werecompared with those of a series of ungrafted, amorphous acryliccopolymers (A1-A10). Three empirical indicators of film properties wereused: crosshatch adhesion, reverse impact resistance and pencilhardness. Adhesion was good in every case; other results are shown inTable 7.

Film properties of the amorphous copolymers were poor. When calculatedT_(g) was below 25° C., the films were very soft, and when it was higherthey were very brittle. When M_(n) was below 30,000 impact resistancewas negligible regardless of T_(g). Copolymer A10 (M_(n) =39,500 andT_(g) =+10 C.) had the best properties in the series, although films aretoo soft for practical use.

Film properties of representative L-C copolymers were substantiallybetter than those of amorphous counterparts (Table 7). Reverse impactresistance of 65 to 80 in-lb is attainable with backbone M_(n) as low as15,000, and pencil hardness of H to 3H is attainable with T_(g) as lowas -10° C.

                  TABLE 7                                                         ______________________________________                                        Comparisons of film properties                                                between amorphous and LC acrylic copolymers:                                  M.sub.n     T.sub.g                                                           (backbone)  (C.)    #PHBA/   Rev. Imp.                                        #     (calcd)       COOH     (in-lb) Hardness                                 ______________________________________                                        Amorphous acrylic copolymers                                                  A1     5,600    30      0      10      H-2H                                   A2     5,200    15      0      10      2B                                     A3    11,000    30      0      10      H-2H                                   A4    15,600    30      0      10      H-2H                                   A5    14,800    15      0      10      B                                      A6    15,100     0      0      (sticky)                                       A7    28,300    20      0      10      2H                                     A8    29,100    10      0      25      B                                      A9    28,900     0      0      (slight sticky)                                A10   39,500    10      0      40      HB                                     LC acrylic copolymers                                                         GB1   14,500    -10       5.2  80      H                                      GB2a  15,130     0        5.0  65      2H                                     GA11  15,700    -10       4.8  70      H                                      GA12  28,450    -10       5.1  80      3H                                     ______________________________________                                         Note: functionality of all the above polymers is 5% by mol.              

It is evident from the above results that films made from L-C acryliccopolymers can have substantially better hardness and impact resistancethan those made from comparable amorphous copolymers.

Preliminary Guidelines for LC Copolymer Design

Having established that liquid crystallinity can dramatically improvefilm properties, a second objective was addressed to develop preliminaryguidelines for copolymer design to optimize film properties ofnon-cross-linked acrylic coatings. Variables studied included M_(n),T_(g), functionality (number of graft segments), flexible spacereffects, and #PHBA/COOH ratio (length of graft segments). Results areshown in Tables 8 through 12.

Effects of M_(n) of ungrafted and grafted acrylic copolymer backbonesare shown in Table 8. T_(g), T_(cl), and adhesion were essentiallyindependent of M_(n) regardless of the presence or absence of flexiblespacer. However, reverse impact resistance and hardness increasedgreatly with M_(n). L-C copolymers with backbone M_(n) of 15,000 and28,000 had excellent reverse impact resistance (>70 in-lb) and goodhardness (H-2H) when T_(g), functionality, and #PHBA/COOH ratio wereoptimal.

                                      TABLE 8                                     __________________________________________________________________________    Effects of acrylic backbone Mn on the film properties of LC copolymers:       Backbone              T.sub.g (C.)                                                                        T.sub.cl                                                                          Rev. Imp.     Crosshatch                      #    Mn     #PHBA/COOH                                                                              (measured)                                                                              (in-lb)                                                                              Hardness                                                                             adhesion                        __________________________________________________________________________    (a). Copolymers with flexible spacer:                                         GB3   5,050 5.1       4     175 35     2B     100%                            B3    5,050 0         0     --  10     (sticky)                                                                             100%                            GB4  10,800 4.9       5     174 60     H      100%                            B4   10,800 0         1     --  10     (sticky)                               GB2a 15,130 4.8       4     174 70     2H     100%                            B2   15,130 0         0     --  10     (sticky)                                                                             100%                            GB5  28,200 5.2       5     174 80     2H     100%                            B5   28,200 0         2     --  20     2B     100%                            (b). Copolymers without flexible spacer:                                      GA13  4,870 5.2       -2    175        (too sticky)                                                                         100%                            A13   4,870 0         -9    --         (too sticky)                                                                         100%                            GA14  9,945 5.0       -3    174 45     HB-H   100%                            A14   9,945 0         -10   --  10     (sticky)                               GA15 14,865 4.9       -2    173 70     H      100%                            A15  14,865 0         -9    --  10     (sticky)                                                                             100%                            GA16 28,500 5.1       -4    174 80     H      100%                            A16  28,500 0         -8    --  30     (sticky)                                                                             100%                            __________________________________________________________________________     Note: The functionality of all the acrylic polymers is 5% by mol.        

T_(g) effects for graft copolymers having a functionality of 5 mol % areshown in Table 9. It can be seen that grafting oligo-PHBA has only aslight effect on T_(g) of the amorphous backbone of the copolymer,increasing it by about 4 to 5 C. Backbone T_(g) has only a modest effecton clearing temperatures (T_(cl)) of the mesophases; T_(cl) increased by6 C. as backbone T_(g) s increased from -10 to +10 C. However, backboneT_(g) substantially affected the empirical film properties. Reverseimpact resistance ranged from poor (<10 in-lb) when backbone T_(g) was10 C. to excellent (>80 in-lb) when T_(g) was -10 C. Hardness increasedwith backbone T_(g).

                                      TABLE 9                                     __________________________________________________________________________    Effects of the acrylic backbone Tg on the film properties of the LC           acrylics:                                                                     T.sub.g (C.)                                                                              After                                                                  Backbone                                                                             Grafting         T.sub.cl                                                                          Rev. Imp.     Crosshatch                     #    (calcd)                                                                              (Measured)                                                                           #PHBA/COOH                                                                              (C.)                                                                              (in-lb)                                                                              Hardness                                                                             Adhesion                       __________________________________________________________________________    GB1  -10    -5     5.2       171 80     H-2H   100%                           GB2a 0      4      5.0       173 65     2H     100%                           GB6  10     14     4.9       177 10     2H-3H  100%                           __________________________________________________________________________

In Table 10, L-C copolymers having different functionalities arecompared. While the reported data were obtained for L-C copolymers withbackbone Mns of about 5,000, similar trends were observed for higherM_(n) s. It can be seen that increasing functionality increased T_(g)and T_(cl). Increasing functionality increased hardness but had anadverse effect on reverse impact resistance. In general, films withfunctionality above 7.5 mol % had poor reverse impact resistance.

                                      TABLE 10                                    __________________________________________________________________________    Effects of functionality on the film properties of the LC acrylic             copolymers:                                                                   Functionality           wt % PHBA                                                                             T.sub.g (C.)                                                                       T.sub.cl                                                                          Rev. Imp.      Crosshatch            #    (mol %)  #PHBA/COOH                                                                              in polymer                                                                            (measured)                                                                             (in-lb) Hardness                                                                             Adhesion              __________________________________________________________________________    GA17 5        4.9       19.9    7    173 35      3B     100%                  GA18 7.5      5.2       25.6    9    174 20      HB     100%                  GA19 10       4.8       32.1    14   181 10      H-2H   100%                  __________________________________________________________________________     Notes: Mn of acrylic backbones is 4,800 ± 300 and calcd Tg is 0 C.    

The effects of the presence of flexible spacer between the acrylicbackbone and the oligo-PHBA segments are exemplified in Table 11. Theflexible spacer reduces the effect of grafting on T_(g). Impactresistance improved when flexible spacer was present. However, theeffect of flexible spacer on reverse impact resistance appeared lesssubstantial when the backbone T_(g) was decreased to about -10 C. Filmswith flexible spacer were slightly softer than those without one.

                  TABLE 11                                                        ______________________________________                                        Effects of flexible spacer on the                                             film properties of the LC acrylic copolymers:                                 T.sub.g (C.)                                                                        Back-   After                 Rev.                                            bone    Grafting  T.sub.cl                                                                           #PHBA/ Imp.  Hard-                               #     (calcd) (measured)                                                                              (C.) COOH   (in-lb)                                                                             ness                                ______________________________________                                        GB2a    0      4        173  4.8    70    2H                                  GA20    0      7        175  4.9    10    2H-3H                               GB1   -10     -5        171  5.0    80    H                                   GA11  -10     -2        173  4.9    70    H-2H                                ______________________________________                                    

Effects of #PHBA/COOH ratio are exemplified in Table 12. As this ratioincreased, T_(g) (after grafting) increased slightly, T_(cl) of L-Cphase increased significantly, reverse impact resistance increasedgreatly, and hardness increased slightly.

                  TABLE 12                                                        ______________________________________                                        Effects of average #PHBA/COOH on                                              the film properties of LC acrylics:                                                                      Rev.        Cross- Ap-                                   #PHBA/   T.sub.g     Imp.  Hard- hatch  pear-                           #     COOH     (C.)   T.sub.cl                                                                           (in-lb)                                                                             ness  adhesion                                                                             ance                            ______________________________________                                        GB2b  3.2      3      159  30    B-HB  100%   TL                              GB2c  4.1      3      164  45    H     100%   OP                              GB2a  4.8      4      174  70    2H    100%   OP                              ______________________________________                                         Notes--                                                                       1. TL = translucent; OP = opaque.                                             2. Acrylic backbone: M.sub.n = 15130, calcd T.sub.g = 0 C., and               functionality = 5% by mol.                                               

Appearance of films were also greatly influenced by the PHBA/COOH ratio.At functionality of 5 mol %, films were translucent when this ratio wasabout 3, but they were opaque when it was 4 or above.

To summarize the observations in this example, it appears that thefollowing guidelines may be useful in designing L-C acrylic copolymersfor coatings binders:

(1) T_(g) of the amorphous part of the copolymer may be low; the optimumfor a given end use may be in the range of -20° to 0° C. Amorphouscopolymers of such low T_(g) are normally far too soft to be usable ascoatings. Acrylic lacquers are usually formulated with T_(g) near orslightly above the highest service temperature. Apparently the presenceof L-C domains can harden low T_(g) films, yet the elasticity associatedwith low T_(g) is at least partly retained.

(2) The best combination of hardness and elasticity is attained whenfunctionality is low but PHBA/COOH ratio is high.

(3) Flexible spacer improves impact resistance when backbone T_(g) is 0C. or higher but has relatively little effect when T_(g) is -10 C.Introduction of flexible spacer by the method used in this study has thedisadvantage of placing relatively unhindered ester groups between theacrylic backbone and the mesogenic group; these ester groups arerelatively vulnerable to hydrolysis in water and weather. Otherpotential routes for introducing flexible spacers are costly. Thus forpractical purposes it may be preferable to use low T_(g) backbones anddispense with flexible spacer.

EXAMPLE 3

In this example it will be demonstrated that the L-C acrylic copolymersof Example 2 can be cross-linked with a melamine resin to provide hard,tough enamels.

Amorphous acrylic copolymers composed of MMA, BA, and acrylic acidhaving calculated T_(g) of -30, -10, and +10 C. and M_(n) of 4,700±200and functionality of 5 mol percent acrylic acid were synthesized asdescribed in Example 2. Each was grafted with PHBA, as described, toprovide L-C graft copolymers having PHBA-COOH ratios of 4±0.2. Liquidcrystallinity was confirmed by polarizing microscopy.

Each of the above copolymers was dissolved or dispersed in a methylisobutyl ketone solution containing HMMM crosslinking resin andp-toluene sulfonic acid (p-TSA) catalyst. The weight ratio was70.6/28.6/0.7 L-C copolymer/HMMM/p-TSA. The mixture was exposed toultrasonic energy to promote mixing. It was cast on untreated,cold-rolled steel panels and baked in a forced air oven for 30 minutesat 150 C. to give a cured film.

Knoop hardness and reverse impact resistance of the 6 enamels weretested as described in Example 2. Results are shown in Table 13.

                  TABLE 13                                                        ______________________________________                                        Copolymer T.sub.g         Reverse Impact                                      and Type     Knoop Hardness                                                                             Resistance                                          ______________________________________                                        -30, Amorphous                                                                             15           80                                                  -10, Amorphous                                                                             17           60                                                  +10, Amorphous                                                                             19           40                                                  -30, L-C     27           80                                                  -10, L-C     34           80                                                  +10, L-C     45            5                                                  ______________________________________                                    

Thus, it is evident that the presence of mesogenic groups improved bothhardness and impact resistance for enamels made from copolymers havingT_(g) s of -30 and -10. When T_(g) is +10, the impact resistance of theL-C film is inferior but the finish is extraordinarily hard. Forcomparison, the hardness of current auto topcoat enamels is about 12 Kn.

In other experiments it was determined that the optimum M_(n) for HMMMcrosslinked L-C copolymers for high-solids enamels is about 5,000. Asshown in Example 2, higher molecular weights are desirable foruncrosslinked enamels.

EXAMPLE 4

L-C telechelic oligoester diols are prepared and cross-linked with aresin, preferably a melamine resin, to provide the coatings of thisexample. After baking, the coatings retained their L-C character whichprovided the improved characteristics to the coatings. The properties ofthe coatings were tested on cold-rolled steel panels.

The ratio of L-C telechelic oligoester diols to resin should be in therange of 95:5 to 50:50, and is preferably about 70:30. The L-Coligoester diols were prepared by reacting4,4'-terephthaloyldioxydibenzoyl (TOBC) with molar equivalents ofaliphatic diols. The general formula is as follows: ##STR90## Wherein,x=1 to 10; ##STR91## R'= O(CH₂)_(n) O,

O[(CH₂)_(n) O]_(m), ##STR92## {O[(CH₂)₅ COO]_(p) R""}₂, orO[R"OOCR'"COO]_(p) R"O;

R" and R""=a aliphatic or cycloaliphatic radical having 12 carbon atomsor less;

R'"=aromatic radical having 10 carbon atoms or less,

cycloaliphatic radical having 12 carbon atoms or less,

or an aliphatic radical having 36 carbon atoms or less;

n=5 to 16; m=2 to 200; and p=1 to 20.

The value of n, sometimes referred to as spacer length, shouldpreferably be in the range of 5 to 12. When n=5 or less, there is poormiscibility in forming enamels and at higher n values mixing becomesincreasingly difficult.

Coatings were prepared by mixing the L-C oligoester diols or polyolsafter solubilization with melamine or polyisocyante resin in thepresence of an accelerator. The coatings were cast on panels and bakedat cross-linking temperatures for testing. L-C oligoester polyols may beprepared by replacing part of the aliphatic diol with a triol or tetrol.

Testing

Proton NMR spectra were recorded at 34 C. on a Varian Associates EM-39090 MHz NMR spectrometer, using Me₄ Si as internal standard. IR spectrawere recorded at 25 C. on a Mattson Cygnus FT-IR using films cast onNaCl plates with polystyrene as standard. A DuPont model 990 thermalanalyzer was used for differential scanning calorimetry (DSC) at heatingrates of 10/min. After the crystalline-mesophase transition temperature(T_(m)) was reached, the temperature was held for 1 min. before the scanwas resumed. Capillary melting points were used to confirm the thermaldata. M_(n) and M_(w) were determined by gel-permeation chromatography(GPC) with a Waters model 520 pump equipped with a model R401 refractiveindex detector, a model M730 data analyzer, and Ultrastragel 100 A, 500A, 1000 A, and 10000 A columns. Mass analysis was performed. A LeitzLabolux miscroscope equipped with a polarizing filter was used foroptical micrographs at 500×magnification; diols were observedimmediately after heating to T_(m), enamels were observed at roomtemperature.

Seven samples of the L-C oligoester diols were prepared and designated1a to 1g, inclusive and, for comparison, seven samples of non L-Coligoester diols were prepared and designated 2a to 2g, inclusive,having corresponding n values and made into amorphous coatings. Thesecorresponding n values are indicated, as follows:

    ______________________________________                                               1a       1b    1c     1d  1e     1f  1g                                       2a       2b    2c     2d  2e     2f  2g                                ______________________________________                                        n =    4        5     6      7   8      10  12                                ______________________________________                                    

In the preparation of the products, reagent materials were used and thesteel panels which were coated were commercially available cold-rolledsteel panels sold under the trademark Bonderite 1000 and having a sizeof 3 inches by 9 inches by 24 GA.

Preparation of 1a-g

TOBC was prepared from terephthaloyl chloride and p-hydroxybenzoic acid(PHBA) as described by Bilibin et al at Polymer Science USSR (1984) 26,2882. TOBC (0.005 mol), diol (0.025 mol), and diphenyl oxide (10 mL)were placed in a 100 mL single-necked round-bottomed flask equipped witha magnetic stirring bar, a distillation adapter, and a septum. The flaskwas flushed with argon for 15 min., and was stirred and heated in an oilbath at 190-200 C. under slow argon flow. The reaction mixture becamehomogeneous after 5 minutes and the evolution of HCl was observed. Thereaction was continued until the evolution of HCl was no longerdetectable by moistened litmus paper (4-5 hr.). The hot reaction mixturewas poured cautiously into 100 mL of toluene and cooled. The oilyresidue that separated was dissolved in CH₂ Cl₂, washed 3 times withwater, and dried over anhydrous MgSO₄. The solution was filtered andconcentrated using a rotary evaporator. The residue was precipitatedfrom methanol. Yields were 87-92% based on TOBC ¹ H NMR for 1c in CDCl₃; 1.4 (broad), 3.6 (triplet), 4.2 (multiplet), 6.8 (doublet), 8.1 ppm(multiplet). FT-IR for 1c: 3420, 2960, 2938, 1720, 1606, 1512 cm⁻¹. L-Cdiols 1a-g had similar spectra.

For comparison to the L-C oligoester diols of this example, non-L-Coligoester diols were prepared from diols in which R=(CH₂)₄ and madeinto amorphous coatings.

Preparation of 2a-g

The diacid chloride precursor was prepared by substituting adipoylchloride for terepthaloyl chloride in Bilibin's procedure. Reaction ofthis precursor with diols was carried out as described for 1a-g exceptthat the products were not poured into toluene. Diols 2a-g were resinoussolids which solidified on standing.

Enamel Formation

Oligoester diols 1b-g and 2a-g, HMMM (hexakis (methyloxy-methyl)melamine resin), methyl isobutyl ketone (MIBK), as a solvent andp-toluenesulfonic acid (p-TSA) as a catalyst were thoroughly mixed in a70/30/30/0.3 wt. ratio. The solution was cast on cold rolled steelpanels and baked at 150 C. for 30 minutes. Less soluble L-C diols 1e-gwere melted, dispersed in solvent, mixed with HMMM and immediately castas films.

Oligoester Diols. The physical properties of 1a-g obtained by GPC, DSCand polarizing optical microscopy are summarized in Table 14.

                  TABLE 14                                                        ______________________________________                                        Physical Properties of 1a-g                                                   diol  n      M.sub.Th.sup.a                                                                       Mn   M.sub.w                                                                             PDI  T.sub.m                                                                            T.sub.i                                                                            texture                         ______________________________________                                        1a    4      550    480  720   1.5  110  204  --                              1b    5      578    530  740   1.4  58   207  smectic                         1c    6      606    570  810   1.4  75   349  smectic                         1d    7      634    610  850   1.4  47   300  smectic                         1e    8      662    650  910   1.4  82   302  smectic                         1f    10     718    680  950   1.4  80   231  nematic                         1g    12     774    720  1130  1.4  90   220  smectic                         ______________________________________                                         .sup.a theoretical molecular weight for x = 0                            

¹ H NMR and 1R spectra were consistent with structures 1a-g and 2a-gassuming that partial chain extension occurred as indicated by GPC. LowM_(n) values and slightly high H analyses suggest that small amounts ofunreacted HO(CH₂)_(n) OH were present in the products.

The L-C nature of 1a-g was demonstrated by DSC (FIG. 10) in which twofirst order transitions were observed; the crystalline-mesophasetransition temperature (T_(m)), and the mesophase-isotropic transitiontemperature (T_(i)). The thermal data revealed an odd-even spacer effectfor T_(m). Smectic-nematic transitions were not evident in the DSC.

In contrast, diols 2a-g were apparently not L-C materials. Only onefirst order transition was observed by DSC.

The mesophases of 1a-g were observed in polarized optical micrographstaken immediately after melting the sample. Textures were identified bycomparing appearance with published micrographs. See: Noel, PolymericLiquid Crystals, Plenum Press, New York, (1984). A nematic texture isobserved for 1f, while more highly ordered smectic textures are observedfor 1b-e and 1g. Crystals were observed by microscopy for diols 2a-g.

Cross-linked Enamels. Diols 1b-g and 2a-g were cross-linked with HMMM at150 C., which falls within the temperature range at which 1b-g areliquid crystalline. Enamel formation of 1a was nearly impossible becauseof its poor miscibility. The properties of the cross-linked enamels aresummarized in Table 15.

                                      TABLE 15                                    __________________________________________________________________________    Properties of Enamels Prepared from 1b-g and 2a-g. Diol:                      HMMM:p-TSA 70:30:0.3 by wt., cure cycle 150/30 min.                                     mesogenic samples             controls                                        1b   1c   1d   1e   1f   1g   2a-g                                  __________________________________________________________________________    spacer length (n)                                                                       5    6    7    8    10   12   4-12                                  reverse impact                                                                          80   50   80   50   50   55   8-15                                  (in-lb)                                                                       direct impact                                                                           80   50   80   50   50   50   10-15                                 (in-lb)                                                                       pencil hardness                                                                         6H   6H   5H   6H   5H-6H                                                                              6H   H-2H                                  (ASTM-D 3363)                                                                 adhesion.sup.a                                                                          5B   5B   5B   5B   5B   5B   5B                                    (ASTM-D 3363)                                                                 acetone rubs                                                                            200  200  200  200  200  200  200                                   (double rubs)                                                                 flexibility                                                                             100% 100% 100% 100% 100% 100% 100%                                  (ASTM-D 522)                                                                  dry film thick..sup.b                                                                   0.5  0.5  0.5  0.5  0.5  0.5  0.5                                   T.sup.c   17   35   23   16   15   22   17-28                                 appearance                                                                              --transparent, glossy--                                             __________________________________________________________________________     .sup.a 5B is 100% crosshatch adhesion;                                        .sup.b units are 1/1000 in.;                                                  .sup.c onset of transition, determined by DSC.                           

As shown in Table 15, all enamels had excellent adhesion, solventresistance, and flexibility. The L-C enamels were far superior tocontrol enamels in both hardness (5H-6H vs. H-2H) and impact resistance(50 to 80 in-lb vs. 8 to 15 in-lb). The odd spacers 1b and 1d affordedthe best properties. Spacer variations did not measurably affect enamelproperties in the control oligoesters.

DSC thermograms of the cross-linked enamels revealed onset of glasstransitions (T_(g)) ranging from T_(g) 15 to 35 for L-C enamels 1b-g andamorphous enamels 2a-g. An odd-even pattern was not observed in eithertype.

Polarized optical micrographs revealed L-C regions in the cross-linkedenamels of 1b-g. Enamels of 2a-g appeared amorphous. IR spectra of thebaked L-C and amorphous enamels had peaks attributable to unreacted OHgroups at 3420 cm⁻¹ (OH stretch) and at 1271 cm⁻¹ (OH bend).

In summary, the method used to make oligoester diols 1a-g was adaptedfrom Bilibin's method for making chain L-C high polymers by using afive-fold excess of HO(CH₂)_(n) OH. Spectral, chromatographic and massanalytical evidence all indicated that the expected products wereobtained from the adapted process.

GPC and analytical data suggested that the structures with x=1 and x=2predominate; smaller amounts of structures with x>1 and of HO(CH₂)_(n)OH are probably present in 1a-g and 2a-g.

The thermal behavior of 1a-g observed by DSC (FIG. 10) confirms thepresence of mesophases and is typical of low molecular weight liquidcrystals. The odd-even effect is of interest because of its directaffect on the physical properties of the L-C diols. The lower T_(m) for1b and 1d is consistent with the higher entropy of activation forcrystallization of odd-n spacers, demonstrated in several main chain L-Cpolymers, Ober et al, Advances in Polymer Science, Liquid CrystalPolymers I, Springer-Verlag (1984), Vol. 59. The apparent absence ofnematic-smetic transitions in the DSC suggests the observed morphologyexists for the entire mesophase.

The nematic texture of oligomeric L-C diol 1f is the same as reportedfor the homologous main chain L-C high polymer, Lenz, Journal PolymerScience, Polymer Symposium (1985) 72, 1-8.

Oligomeric diols 1b-d were soluble in MIBK and were miscible with theHMMM cross-linker; films were readily cast. Higher melting diols 1e-gwere less miscible, but the consistently good film properties indicatethat adequate mixing was achieved. Mixing of diol 1a with HMMM wasinadequate to produce uniform films.

Enamels made from odd-n L-C diols 1b and 1d had better impact resistancethan those made from even-n diols. This effect may be attributed to anodd-even effect, although other variables may be involved.

The enhanced properties of the L-C diol enamels are not simplyexplainable by the monomer raising the T_(g) of the coating. In fact,T_(g) s of the cross-linked enamels of 1b-g are abnormally low for hardcoatings, and are similar to the much softer control enamels.

EXAMPLE 5

A non-L-C linear oligoester diol is prepared by heating a mixture ofphthalic acid (PA), adipic acid (AA) and neopentyl glycol (NPG). Thereaction of the mixture is effected under N₂ at 230 C. with removal ofH₂ O until the acid number was less than 10 mg KOH/g. The sum of themols of acids should be less than the mols of diols and the ratio shouldbe in the range of 1:2 to 1:1.1. A particular example of a mixture ofPA, AA and NPG at a mol ratio of 1:1:3 was highly satisfactory.

A mixture of the diol or polyol, PHBA, an acid catalyst and particularlyp-TSA and solvent was heated under N₂ in a 3-neck flask equipped withstirrer, Dean-Stark trap, condenser and thermometer. The PHBA was insubstantially pure form so as not to affect catalytic action. ThePHBA/diol or PHBA/polyol weight ratio varied from 20/80 to 60/40, butthe preferred ratio is about 40/60; 0.2 weight % of p-TSA was used as anacid catalyst to provide a predominantly phenolic L-C oligoester diol orpolyol. About 10 weight % of solvent was used; the amount was adjustedto maintain the temperature in the range of 210° C. to 250° C., andpreferably in the range of 227° to 233° C. In an actual preparation thetemperature was held at 230±3 C. Distillate (cloudy H₂ O) was collectedin the Dean-Stark trap during 9 to 11 hr. The reaction mass was cooledto 115 C, and MIBK was added to yield a solution (20/80 PHBA/diol ratio)or suspension (other PHBA/diol ratios) of the crude L-C polyol. Apreferred solvent is "Aromatic 150" sold by Exxon.

It is important that the acid catalyst be used and that the temperaturebe controlled to provide the L-C predominately phenolic oligoesters ofthe invention. Likewise, it is important that the PHBA be used in theweight ratio range specified to give the L-C diols desired.

The linear oligoester diol was heated with salycilic acid and with MHBAusing a similar procedure to yield modified polyols. 60% to 80% oftheoretical distillation was obtained.

Purification

The crude L-C polyols made from 20/80 and 30/70 PHBA/diol ratios wereconcentrated and dissolved in CH₂ Cl₂. The solution was washed 5 timeswith H₂ O, dried with Na₂ SO₄, and concentrated on a rotary evaporator.The residues were heated at 120 C. to constant weight. The crude L-Cpolyols made from 40/60 to 60/40 ratios were purified similarly but werenot washed with water. They were heated at about 80 C. under vacuum on arotary evaporator to remove small amounts of volatile, crystallinematerial.

Enamel Preparation

Solutions or mixtures of L-C polyol, HMMM and p-TSA in a 75/25/0.25weight ratio were cast on cold-rolled panels and baked at 175 C. for thespecified time. Dry film thicknesses were 20 to 25 μm.

Characterization and Testing

IR spectra were recorded using a Perkin-Elmer 137 NaCl-prismspectrophotometer. A DuPont model 990 thermal analyzer was used fordifferential scanning calorimetry (DSC) at heating rates of 10/min.After the crystalline-mesophase transition temperature (T_(m)) wasreached, the temperature was held for 1 min. before the scan wasresumed. Capillary melting points were used to confirm the thermal data.M_(n) and M_(w) were determined by gel-permeation chromatography (GPC)with a Waters model 520 pump equipped with a model R401 refractive indexdetector, a model M730 data analyzer, and Ultrastragel 100 A, 500 A,1000 A and 10000 A columns. Mass analysis was performed. A Leitz Laboluxmicroscope equipped with a polarizing filter was used for opticalmicrographs at 500× magnification; L-C polyols were cast on glass slidesand were dried and observed at 25 C., and enamels were baked at 175 C.for 20 minutes on the glass slides.

Hydroxyl numbers were determined by the pyromelliticdianhydride/imidazole method. See: Demarest, B. O.; Harper, L. E.Journal of Coating Technology 1983, 55(701), 65-77. Impact resistanceand pencil hardness were tested according to ASTM-D 2793 and ASTM-D3363, respectively. Solvent resistance was tested by spotting films withmethyl ethyl ketone. Potentiometric titration in DMF indicated that asubstantial fraction of phenolic groups are present in the oligomers,but it has not yet been feasible to reproducibly obtain quantitativeresults because precipitate formed during titration.

This preparation yields PHBA-modified oligomers, apparently with sidereactions. The odor of phenol was barely detectable in the products,indicating that little phenol had been formed. p-TSA catalyst plays acrucial role. When p-TSA was not used in the 30/70 PHBA/diol reactiononly 75% of theoretical distillate was collected, and the productsmelled strongly of phenol. Solvent also plays an important role byhelping control temperature and by facilitating removal of water. Ifdesired, the products can be purified as described to remove smallamounts of unreacted PHBA and possibly of phenol.

Modification of the PA/AA/NPG diol with salicylic and m-hydroxybenzoicacids apparently did not proceed as smoothly as the modification withPHBA. No liquid crystals could be detected in the products by polarizingmicroscopy.

Potentiometric titration and infrared spectra (peak at 3400 cm⁻¹)indicate that phenolic end groups predominate in the product oligomers.

Molecular weights determined by GPC are provided in Table 16. Alsoprovided are rough estimates of the average number of PHBA units pernumber average molecule. These estimates were obtained by multiplyingproduct M_(n) by the weight fraction of PHBA charged and dividing theresult by 120, the molar mass of PHBA minus water.

                  TABLE 16                                                        ______________________________________                                        Gel Permeation Chromatography of Polyols                                      PHBA/diol                                                                             ratio                      avg PHBA                                   wt.     mol     M.sub.n                                                                              M.sub.w                                                                             M.sub.w /M.sub.n                                                                    residue/molecule                           ______________________________________                                         0/100  --      1200   2000  1.7   --                                         20/80   2.1/1   1400   2400  1.7   2.3                                        30/70   3.6/1   1100   1900  1.7   2.8                                        40/60   5.8/1    970   1600  1.6   3.2                                        50/50   8.8/1    870   1400  1.7   3.6                                         60/40*  13/1    830   1400  1.7   4.1                                        ______________________________________                                         *Filtered to remove a small fraction of THFinsoluble material.           

The L-C character of PHBA-containing oligomers was demonstrated bypolarizing microscopy as indicated in Table 17.

DSC data in Table 17 indicate that T_(g) increases with increasingPHBA/diol ratios except for the 60/40 PHBA/diol ratio.

                  TABLE 17                                                        ______________________________________                                        Differential Scanning Calorimetry                                             and Polarizing Microscopy of Polyols                                                 PHBA/diol ratio                                                                 0/100   20/80   30/70 40/60 50/50 60/40                              ______________________________________                                        T.sub.g (C.)                                                                           -10     7       14    19    27    14                                 Appearance,                                                                            clear   a few   L-C   L-C   L-C   L-C                                500×       spots                                                        ______________________________________                                    

Enamel Coatings Properties

Clear coatings were formed by cross-linking the PHBA-modified oligomerswith a standard melamine resin. Baking at 175 C. was necessary to obtainoptimal properties. The cured films were nearly transparent and glossyexcept for films made from 60/40 PHBA ratio L-C polyol. Adhesion wasexcellent.

The outstanding feature of enamels made from 40/60 to 50/50 PHBA/diolratio L-C polyols is that they are both very hard and very impactresistant as shown in Table 18.

                  TABLE 18                                                        ______________________________________                                        Impact Resistance and Pencil Hardness of Baked Enamels                        Baking Time                                                                   (min)    PHBA/diol ratio                                                      at 175 C.                                                                              0/100   20/80   30/70 40/60 50/50 60/40                              ______________________________________                                        20       *(HB)   p(H)    p(H)  p(3H) p(4H) f(5H)                              40       *(HB)   p(H)    p(H)  p(3H) p(4H) f(5H)                              60       *(HB)   f(H)    p(2H) p(4H) f(5H) f(6H)                              ______________________________________                                         p: passes 80 inlb reverse impact test; f: fails;                              *: appears to pass but cracks after standing several days.               

The enamels described in Table 18 with pencil hardness of 3H to 6H hadexcellent solvent (methyl ethyl ketone) resistance.

The salycilic acid modified oligomers did not cure at 175 C. The MHBAmodified oligomers cured at 175 C. to give hard films, but all failedthe 80 in-lb impact resistance test.

Polarizing micrographs showed clear evidence of the presence ofbirefringent phases in enamel films made from polyols modified by 30percent or more of PHBA. L-C regions were not visible in cured filmsmade from the PA/AA/NPG polyol or from the MPHA-modified enamels.

The results of the above experiments indicate that mesogenic groupssubstantially enhance a polymer resin's coating quality. Graftingoligomeric segments derived from PHBA or TPA/PHBA onto coating resinsyields resins that contain liquid crystalline (L-C) phases. These phasesimpart at least three benefits: "solution" viscosity is reduced by theformation of non-aqueous dispersions, dry-to-touch times are sharplyreduced, and films are both hardened and toughened. Imparting L-Ccharacteristics to a resin minimizes the hardness/impact resistancetradeoff necessary with non-modified coating resins.

Although the invention has been described with regard to its preferredembodiments, it should be understood that various changes andmodifications as would be obvious to one having the ordinary skill inthis art may be made without departing from the scope of the inventionwhich is set forth in the claims appended hereto.

The various features of this invention which are believed new are setforth in the following claims.

What is claimed is:
 1. A polymeric vehicle which when applied to asubstrate provides a coating binder having a Tg not greater than about60° C., a pencil hardness of at least about H, and a reverse impactresistance of at least about 30 inch-lbs. at a binder thickness of about1 mil, said polymeric vehicle comprising:(a) from about 100 to about 35weight percent, based upon the weight of the polymeric vehicle, of amodified polymer, said modified polymer being a polyester polymercovalently bound to at least one mesogenic group selected from the groupconsisting of: ##STR93## (b) from about 0 to about 65 weight percent,based upon the weight of the polymeric vehicle, of a compositionselected from the group consisting of cross-linker resin, unmodifiedpolymer resin, and mixtures thereof and wherein the modified polymer ismodified to contain about 5 to about 50 weight percent mesogenic groups.2. A polymeric vehicle as recited in claim 1 wherein the polymericvehicle includes a cross-linker resin.
 3. A polymeric vehicle as recitedin claim 2 wherein the cross-linker resin is selected from the groupconsisting of aminoplast resins, polyisocyanate resins and mixturesthereof.
 4. A polymeric vehicle as recited in claim 1 wherein themesogenic groups are grafted onto the polyester polymer to provide themodified polymer.
 5. A polymeric vehicle as recited in claim 4 whereinthe polyester polymer is provided with carboxylic functional groups byreacting the polyester polymer with a dicarboxylic acid or anhydride toprovide the polymer with reactive sites for reaction with the mesogenicgroups.
 6. A polymeric vehicle as recited in claim 1 or 5 wherein thepolyester polymer is an alkyd polymer.
 7. A polymeric vehicle as recitedin claim 5 wherein the dicarboxylic acid or anhydride is selected fromthe group consisting of terephthalic acid, adipic acid, isophthalicacid, succinic acid, succinic anhydride, phthalic acid, phthalicanhydride, maleic acid, maleic anhydride and mixtures thereof.
 8. Apolymeric vehicle as recited in claim 1 wherein the polyester polymerhas a number average molecular weight in a range of from 500 to 20,000.9. The polymeric vehicle of claim 1 wherein the polyester polymer isprepared by reacting a polyacid with a polyol.
 10. The polymeric vehicleof claim 9 wherein the polyacid is a dicarboxylic acid having a carbonchain length of from 4 to
 36. 11. The polymeric vehicle of claim 10wherein the polyacid is selected from the group consisting ofisophthalic acid, terephthalate acid, fumaric acid, HOOC(CH₂)_(n) COOH,maleic acid, phthalic acid, hexahydrophthalic acid and trimellitic acidand anhydrides of maleic acid, phthalic acid, hexahydrophthalic acid andsuccinic acid where n=2 to
 14. 12. A polymeric vehicle as recited inclaim 1 or 3 wherein one or more of the mesogenic groups is terminatedwith --H, --CN, ##STR94## and --OR, wherein R is selected from the groupconsisting of H, a straight chain and branched alkyl group having 1 to12 carbon atoms and an aryl group having 6 to 12 carbon atoms.
 13. Thepolymeric vehicle as recited in claim 1 wherein the modified polymer isa polyester polymer which has a number average molecular weight of aboveabout 7,000 and the polymeric vehicle is free from cross-linker resin.